As one of gradation display systems, there is a frame rate control system (FRC) for performing gradation expression by using a plurality of frames and controlling a column voltage every frame. In the case where the gradation display is performed under the frame rate control, flickers are reduced by preventing the number of ON and OFF patterns from varying.
In the case of performing gradation expression under the FRC (Frame Rate Control), when the number of display gradations increases, flickers easily occur because a gradation occurs in which the ratio between the number of times of ON and the number of times of OFF decreases. Though there is a method of reducing the number of flickers by increasing a frame rate, power consumption increases. For example, though gradations are expressed by seven frames in the case of 256-color display, 15 frames are necessary for 4,096-color display, and in order to simply equalize flicker levels, it is necessary to almost double a frame rate. On the other hand, power sources are limited in the case of mobile terminals including a portable telephone and it is requested to reduce power consumption. Moreover, a circuit for preventing a flicker must be simple from the viewpoint of requests for reduction of display-device frame in size and reduction of cost. Moreover, to realize multi-color, a frame frequency exceeds 200 Hz and it is impossible to reduce power consumption by the FRC.
Moreover, in realizing multi-color by the pulse-width modulation method, a problem occurs that power consumption is increased because the number of times of charge and discharge of a segment signal line is increased due to the increase of the number of pulses to be applied in one horizontal scanning period, or a waveform deterioration due to a product of a capacity of a wiring resistance and a resistance thereof deteriorates the gradation characteristic because a display device has a capacitive load in general and a pulse width is narrowed.
The present invention has been made to solve the above problems, and in order for driving at a low frame frequency, different ON/OFF patterns are used every N line, every frame, every display color, and between even rows and odd rows in the FRC. In order to realize the multi-color and reduction in power supply, a gradation expression by the FRC and a gradation expression system by the pulse-width modulation (PWM) method or pulse-height modulation (PHM) method are combined to thereby suppress the increase of the frame rate due to the increase of the number of the display gradations, and the present invention has its object to provide a display device, capable of realizing low power and displaying multi-color.